This Chandra image marks the
deepest X-ray look at the "zone of avoidance" -- a
region of space behind which no optical observation has
ever been taken because thick clouds of dust and gas in
the spiral arms of the Milky Way block visible
radiation. X-rays, along with certain radio and
infrared wavelengths, can penetrate this barrier, and
Chandra provided the best look yet at what X-rays
reveal. The diffuse blue emission is due to hot (ten
million degree Celsius) gas concentrated along the
plane of the Galaxy.

Most of the pink and red objects sources in this image
are believed to be active stars in our Milky Way
galaxy. The blue objects, referred to as "hard" sources
because they emit more energetic X-rays, are considered
to be distant galaxies. Because astronomers were able
to identify these objects as being well beyond the
galactic plane, they were able to determine that the
X-ray glow from the galactic plane comes not from
individual sources, but from the hot diffuse gas.

Chandra observed this region of the galactic plane in
the constellation Scutum on February 25-26, 2000, with
its Advanced CCD Imaging Spectrometer instrument for a
total exposure time of 90,000 seconds.